The present invention relates to a connection mechanism, in particular for an earth-working machine.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
The term “earth-working machine” refers according to the invention to machines transferring drive power from a drive system via a rod assembly to a tool arranged on a rod assembly. In particular, these machines include earth boring machines configured to introduce subsurface boreholes and in particular horizontal boreholes into the ground. Typically, thrust forces or pressure forces and a drive torque are transmitted via the rod assembly of the earth boring machine to the tool constructed as a drill head. However, earth-working machines also exist where only thrust forces or pulling forces are transferred via the rod assembly to a corresponding tool. These include, in particular, those earth-working machines with which existing boreholes in the ground or already installed old conduits can be expanded or pulled out, wherein optionally a new pipe can be pulled in at the same time. The earth-working machines are frequently also configured so that they can be used both for creating the subsurface boreholes as well as for pulling work, i.e. for expanding an existing borehole or an old conduit and/or for pulling in the new pipe. It then becomes possible to first create a pilot borehole with the same earth-working machine, wherein a pilot drill head is pushed through the ground until it reaches a destination pit, and the pilot drill head is replaced in the destination pit by an expansion head, wherein the pilot bore hole is expanded when the rod assembly is pulled back. Optionally, a new pipe attached to the expansion head can be pulled into the expanded subsurface borehole simultaneously with the expansion head.
The term “drive section” according to the invention refers to an extension or a plug and/or screw element for a drive, for example a linear motor or a rotary motor, of a machine, in particular an earth-working machine. The drive section may, for example, be a connection element screwed onto a drive shaft of a rotary motor. The drive may produce the thrust, pressure and pulling forces as well as a rotational force or a rotational torque required for operating the machine. The pulling force is required, for example, wherein a new pipe is pulled in with an earth-working machine. Transmitting a torque is important, for example, with an earth boring machine in the technical field of horizontal drilling.
The rod assembly of such earth-working machines is usually formed of a plurality of rod sections which are sequentially connected with one another during the drilling advance. The individual rod sections are connected with coupling elements, wherein in addition to plug couplings, as described in DE 196 08 980 A1, in particular screw connections are frequently used. Screw connections have the significant advantage of low manufacturing costs and the option to form the screw connections automatically. However, screw connections have a significant disadvantage in that they frequently represent the weakest points of the rod assembly, due to the relatively small diameter in the region of the threaded plug of the threaded connection and the geometry-related large notch effect of the thread itself.
Conventional types of threads most frequently used for rod assemblies of earth-working machines are API threads and round threads according to DIN 20 400. The useful life of such thread shapes, however, has turned out to be too short for day-to-day operations of the earth-working machines.
It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide an improved connection with an improved lifetime, which has an increased lifetime in particular when used for connecting a drive section with a shaft element of a rod assembly of an earth-working machine, and which in addition to the increased lifetime simultaneously allows rapid change, i.e. rapid detachment and attachment, of the elements to be connected.